Messages in this thread | | | Date | Wed, 2 May 2018 09:44:25 +1000 | From | "Tobin C. Harding" <> | Subject | Re: [PATCH 2/3] random: Return nbytes filled from hw RNG |
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On Wed, May 02, 2018 at 09:33:39AM +1000, Tobin C. Harding wrote: > Currently the function get_random_bytes_arch() has return value 'void'. > If the hw RNG fails we currently fall back to using get_random_bytes(). > This defeats the purpose of requesting random material from the hw RNG > in the first place. > > There are currently no intree users of get_random_bytes_arch(). > > Only get random bytes from the hw RNG, make function return the number > of bytes retrieved from the hw RNG. > > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> > Signed-off-by: Tobin C. Harding <me@tobin.cc> > --- > drivers/char/random.c | 16 +++++++++------- > include/linux/random.h | 2 +- > 2 files changed, 10 insertions(+), 8 deletions(-) > > diff --git a/drivers/char/random.c b/drivers/char/random.c > index 031d18b31e0f..3a66507ea60b 100644 > --- a/drivers/char/random.c > +++ b/drivers/char/random.c > @@ -1725,26 +1725,28 @@ EXPORT_SYMBOL(del_random_ready_callback); > * key known by the NSA). So it's useful if we need the speed, but > * only if we're willing to trust the hardware manufacturer not to > * have put in a back door. > + * > + * Return number of bytes filled in. > */ > -void get_random_bytes_arch(void *buf, int nbytes) > +int __must_check get_random_bytes_arch(void *buf, int nbytes) > { > char *p = buf; > + int left = nbytes; > > - trace_get_random_bytes_arch(nbytes, _RET_IP_); > - while (nbytes) { > + trace_get_random_bytes_arch(left, _RET_IP_); > + while (left) { > unsigned long v; > - int chunk = min(nbytes, (int)sizeof(unsigned long)); > + int chunk = min(left, (int)sizeof(unsigned long)); > > if (!arch_get_random_long(&v)) > break; > > memcpy(p, &v, chunk); > p += chunk; > - nbytes -= chunk; > + left -= chunk; > } > > - if (nbytes) > - get_random_bytes(p, nbytes); > + return nbytes - left; > } > EXPORT_SYMBOL(get_random_bytes_arch); > > diff --git a/include/linux/random.h b/include/linux/random.h > index 2ddf13b4281e..308168c0a637 100644 > --- a/include/linux/random.h > +++ b/include/linux/random.h > @@ -38,7 +38,7 @@ extern void get_random_bytes(void *buf, int nbytes); > extern int wait_for_random_bytes(void); > extern int add_random_ready_callback(struct random_ready_callback *rdy); > extern void del_random_ready_callback(struct random_ready_callback *rdy); > -extern void get_random_bytes_arch(void *buf, int nbytes); > +extern int get_random_bytes_arch(void *buf, int nbytes); > > #ifndef MODULE > extern const struct file_operations random_fops, urandom_fops; > -- > 2.7.4 >
Tested by loading a module with this init funciton
static int __init test_init(void) { const int size = 256; char buf[size]; int got;
pr_info("test: module inserted\n");
got = get_random_bytes_arch(buf, size); if (got != size) pr_warn("get_random_bytes_arch() failed, got %d bytes\n", got);
return 0; } module_init(test_init);
Fails on machine without RDRAND and succeeds on machine with RDRAND
thanks, Tobin.
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